The ships entered the area around noon on Monday and left in the early hours of Tuesday, the officials said.

China's State Oceanic Administration confirmed four Chinese marine surveillance ships were patrolling waters near the islands.

But China routinely maintains such ships are in Chinese waters and a Chinese official accused Japan of intrusion.

"Japan has continued to ignore our warnings that their vessels and aircraft have infringed our sovereignty," the Communist Party chief of China's marine surveillance corps, Sun Shuxian, said in an interview posted on the Oceanic Administration's website.

"This behavior may result in the further escalation of the situation at sea and has prompted China to pay great attention and vigilance," Sun was quoted as saying.

Sino-Japanese ties chilled after the Japanese government bought the disputed islands, known as the Senkaku in Japan and Diaoyu in China, from a private Japanese owner last September.